[FFmpeg-user] VBR encoding for libsvtav1.

[Ferdi Scholten]

On Mon, 27 Nov, 2023, 7:32 am Aditya Dandavate, 
<adityadandavate04 at gmail.com>
> wrote:
>
>> On Mon, 27 Nov, 2023, 4:16 am Ferdi Scholten,<ferdi at sttc-nlp.nl>  wrote:
>>
>>> What is the quality rate control when encoding in VBR mode ?
>>>> I get message :
>>>>
>>>> Svt[warn]: The input q value is ignored in vbr mode 20 when I set the
>>> -crf
>>>> to 20 when enabling the -svtav1-params rc=1.
>>>> When I set -qp 20, the conversion fails.
>>>>
>>>> Which mode to set quality when encoding in VBR mode ?
>>>>
>>> vbr encoding does not support quality setting, you get the maximum
>>> quality that fits the specified bitrate and it uses lower bitrates if
>>> possible if the content does not require high bitrates.
>>>
>>>
>>> If you want CRF with a cap on the bitrate you need to set mbr
>>> (MaximumBitRate)
>>>
>>>       -crf 20 -svtav1-params mbr=5000k
>>>
>>> You do not need to specify rc=0, because that is default. You also do not
>>> specify -b:v 5000k
>>>
>>>
>>> Or if you want VBR
>>>
>>>       -svtav1-params rc=1 -b:v 5000k
>>>
>>> No quality settings like crf or qp as they require rc=0 you can however
>>> set -qmin (default 1) and -qmax (default 63)
>>>
>>>
>>> OR if you want CQP
>>>
>>>       -qp 20 -svtparams aq-mode=0 -b:v 5000k
>>>
>>> qp only works when aq-mode=0 (default aq-mode=2)
>>>
>>>
>>> Hope that helps?
>>
> Also, a quick question about Constrained Quality Mode:
>
> In VP9, we trigger it by combination of '-crf' and 'b:v' and the value of
> bitrate is must be non zero to trigger the mode.
>
> How to trigger it in libsvtav1 ?
>
by setting -qp AND aq-mode=0 AND bitrate